1. Field of the Invention
The present invention relates to straightness measuring devices, and more particularly for measuring the straightness of a rail at its welding area.
2. Discussion of the Related Art
In laboratories, various methods for measuring and controlling the straightness of an object are used. These methods implement systems Which are too complex or too bulky to be used outside the laboratory, for example, for measuring on site the straightness of a rail, or any other object, fixed or too bulky to be transported into a measuring laboratory.
It is important to control the straightness of a rail, after welding and grinding, to ensure that important deformations do not cause vibrations due to the passage of trains.
FIG. 1 schematically represents a conventional device for measuring the straightness of a rail. It is a so called GEISMAR ruler. This device includes a frame (not shown) provided with two feet 10 which are placed on a rail 12. A belt 14 is tightened between two pulleys 16 and 17 parallel to the rail 12. One pulley, 16, is provided with a crank 16-1 to draw, parallel to the rail 12, a carriage 18 fixed to belt 14. Carriage 18 is guided by slippers (not shown) which must be very carefully fabricated because their straightness must be very accurate. Carriage 18 is provided with a sensor 18-1 biased toward the rail 12.
To measure the straightness of a rail 12, especially at a welding 12-1, an operator acts upon the crank 16-1 to move the carriage 18 from one pulley to the other. During this motion, a stylus (not shown) actuated by sensor 18-1 through a rod system, draws the profile of the rail onto a paper strip which is unrolled while carriage 18 is moving.
A first drawback of this device is its weight (at least two persons are needed to carry it) because, to ensure a sufficient accuracy, the device has a rigid structure, which makes necessary to use solid steel parts.
A second drawback of such a device is its fragility. Its accuracy may be easily ruined, for example, due to shocks or due to the fact that it was placed in an unstable position during its transport or its storage. Once the accuracy of such a device is ruined, it is practically impossible to correct it. A standard template of the device must be established; this template must be subtracted for each measured profile of a rail to obtain the real profile of the rail.